Correspondence: Navdeep Tangri, Seven Oaks General Hospital, 2LB10-2300 McPhillips St., Winnipeg, MB R2V 3M3, Canada. E-mail: ntangri@sogh.mb.ca Kidney International (2019) 96, 247–248; https://doi.org/10.1016/ j.kint.2019.03.011 Copyright ª 2019, International Society of Nephrology. Published by Elsevier Inc. All rights reserved. The choice of the assay for measuring albumin has a major impact on routine laboratory values To the editor: In their recent study comparing different assays to measure albumin level, van de Logt et al. 1 show that the use of bromocresol green (BCG) (but not bromocresol purple [BCP]) leads to a substantial overestimation of plasma and serum albumin concentration (mean bias: 6.2 g/l), in comparison to the reference immunonephelometric assay in patients with hypoalbuminemia (including patients with membranous nephropathy, liver cirrhosis, or sepsis) and in chronic kidney disease patients with albumin concentrations within reference values. The investigators pointed out that up to 59% of patients with membranous nephropathy would receive inappropriate prophylactic anticoagulant therapy on the basis of albumin measured by BCG assay. Ten years ago, we similarly demonstrated substantial discrepancies in calcium classification according to Kidney Disease Outcomes Quality Initiative targets 2 in 89 patients on chronic hemodialysis, when correcting total calcium level for albumin level measured by BCG versus BCP assay. 3 Indeed, as compared with BCG, hypercalcemia was diag- nosed in 20% of patients when albumin was measured by BCP. Moreover 12% of patients were classified as hypocal- cemic with BCG but had normal adjusted calcium levels with BCP. In conclusion, the choice of either BCG or BCP has a major impact on several laboratory parameters (i.e., not only albumin concentration itself but also albumin-corrected cal- cium levels) used to manage multiple conditions. The type of albumin assay used should be clearly indicated in any study or clinical setting and its impact taken into account to avoid inappropriate clinical decisions or conclusions. 1. van de Logt A-E, Rijpma SR, Vink CH, et al. The bias between different albumin assays may affect clinical decision-making. Kidney Int. 2019;95: 1514–1517. 2. National Kidney Foundation. K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease. Am J Kidney Dis. 2003;42(suppl 3):S1–S201. 3. Labriola L, Wallemacq P, Gulbis B, Jadoul M. The impact of the assay for measuring albumin on corrected (“adjusted”) calcium concentrations. Nephrol Dial Transplant. 2009;24:1834–1838. Laura Labriola 1 and Michel Jadoul 1 1 Department of Nephrology, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Brussels, Belgium Correspondence: Laura Labriola, Cliniques Universitaires Saint-Luc, Uni- versité Catholique de Louvain, Avenue Hippocrate 10, 1200 Bruxelles, Belgium. E-mail: laura.labriola@uclouvain.be Kidney International (2019) 96, 248; https://doi.org/10.1016/j.kint.2019.04.007 Copyright ª 2019, International Society of Nephrology. Published by Elsevier Inc. All rights reserved. Albumin assays and clinical decision-making in nephrotic syndrome patients To the editor: With interest, we have read the article by van de Logt et al., 1 in which the importance of albumin assays in assessing hypoalbuminemia in nephrotic syndrome was highlighted. The investigators confirm the known bias for the various (dye binding) albumin assays and plead for improved standardization. We do not believe that improved standardizing albumin assays is the key to better management of hypoalbuminemia. The International Federation of Clinical Chemistry/Bureau Communitaire de Réference/College of American Patholo- gists CRM 470 standard was a quantum leap in albumin standardization, an approach that can hardly be improved in the near future. Aspecificity of colorimetric albumin assays remains an issue that is hard to solve by standardization. Confounders comprise carbamylation, 2 uremic toxins (e.g., para-cresyl sulfate, 3 and a 2 -macroglobulin concentration. 4 The altered plasma protein spectrum in nephrotic syndrome (higher a 2 -macroglobulin–albumin ratio) highlights the analytical failure of the dye binding assays. The acute phase protein a 1 -acid glycoprotein 3 affects albumin test results when using bromocresol-based dyes. The incon- stant analytical interferences lead to variations that cannot be corrected for by standardization. As variations in car- bamylation and plasma protein spectra do not directly depend on albumin concentrations, a mathematical bias correction of albumin (as would be the case in conse- quence of restandardization) in nephrotic syndrome is inappropriate. In our database, the determination coeffi- cient between urea and albuminemia in nephrotic syn- drome was only 0.01. Therefore, a robust immunochemical method (immu- nonephelometry, immunoturbidimetry) should be the preferred method for measuring albumin. 2 Harmonization to immunological albumin assays rather than standardi- zation should be advocated to promote interchangeability of test results and eventually improve treatment of patients. 1. van de Logt A-E, Rijpma SR, Vink CH, et al. The bias between different albumin assays may affect clinical decision-making. Kidney Int. 2019;95: 1514–1517. 2. Kok MB, Tegelaers FP, van Dam B, et al. Carbamylation of albumin is a cause for discrepancies between albumin assays. Clin Chim Acta. 2014;434: 6–10. letters to the editor 248 Kidney International (2019) 96, 245–251